The N-S trending Manhuaçu-Santa Margarida shear zone system extends for ca. 300 km in eastern Minas Gerais. As one of the main structures of the crystalline core of the Neoproterozoic Araçuaí Orogen, the Manhuaçu-Santa Margarida system is made up of a series of ductile shear zones, which show a sigmoidal trace in map view. The northern segment of the system mainly consists of west-verging thrusts and subordinate dextral strike-slip shear zones. The central and southern segments are dominated by dextral strike-slip shear zones. The development of the Manhuaçu-Santa Margarida system occurs in four distinct Neoproterozoic deformation phases. During the first phase, the system nucleated as a series of thrust shear zones, which remain preserved in the northern segment. During the second phase, the thrust zones experienced a clockwise rotation coupled with an intensive strike-slip reactivation, becoming vertical and NE-striking in the southern portion of the orogen. The third deformation phase generated normal-sense shear zones, observed only in the northern segment of the system. Brittle deformation along WNW-striking fault zones and jointing are the manifestations of the fourth and youngest deformation phase. The southern segment of the Manhuaçu-Santa Margarida system, dominated by dextral strike-slip zones, rotates progressively to a NE orientation and merges with the structures of the northwestern segment of the Ribeira belt. Therefore, the structures of the southern termination of the Manhuaçu-Santa Margarida system are of the same age or slight older than the dextral strike-slip shear zones that characterize the tectonic grain of the northwestern portion of the Ribeira Belt.
Strike-slip shear zones; Araçuaí orogen; Ribeira belt; Brasiliano
